This invention relates to a microfistula tube for the creation of microfistulae within the body, to be used for example to drain unwanted aqueous fluid, and a method and apparatus for the insertion into the body of a microfistula tube. In a preferred embodiment the microfistula tube is used for drainage of excess fluid in the eye.
Existing devices for the drainage of excessive aqueous fluid within the body, and most especially to control intraocular pressure in advanced refractory glaucoma, have been made of materials such as horse-hair, silk thread, gold foil, autologous canaliculus, tantalum wire, glass, platinum, polymethylmethacrylate, polyethylene, gelatin and autologous cartilage. Various devices made of these materials have been inserted, for example, in the anterior chamber of the eye under a conjunctival or scleral flap extending into the anterior subconjunctival space. However, problems frequently associated with existing devices include foreign-body reactions leading to fibroblast proliferation and sub-conjunctival fibrosis formation around the posterior exit of the drainage implant. Commonly, existing devices require large incisions of 1 mmxc3x973 mm or even larger. Such incisions represent an extensive surgical injury and can lead to the formation of excessive quantities of scar tissue. Further, existing fistula tubes are mainly of non-biological materials and operate in far from physiological conditions. Such a fistula tube may generate an adverse tissue response, which causes blockage of the fistula tube resulting in uncontrolled eye pressure and ultimately negates any beneficial effects. More recent developments have attempted to protect the posterior exit of the drainage tube and develop posterior shunting of aqueous fluid to an equatorial sub-Tenon""s collecting device.
These developments include a modified Krupin-Denver valve, the Schocket implant, the Joseph valve, and the Molteno implant.
An object of the present invention is to provide a biological microfistula tube subject to reduced rejection effects, that will lead to the formation of a microfistula for permanent or long-term aqueous fluid bypass, with minimal overdraining, and tending to impede wound healing processes and hence the closure of the drainage pathway. Further objects of the invention are to provide such a biological microfistula tube generating minimal tissue reaction, and matching outflow resistance, to allow the control of eye pressure and reduce surgical complications. A further object of the present invention is to provide a method and apparatus for the implantation of the biological microfistula tube.
According to a first broad aspect of the present invention there is provided a microfistula tube including:
a soluble duct, defining a drainage canal having an inner surface, the duct being biocompatible, wherein
said microfistula tube is coated with and/or incorporates biological cells for forming a basement membrane, or an intracellular matrix and a basement membrane.
Preferably the biological cells coat the inner surface of the drainage canal.
Preferably the microfistula tube is made of a mouldable material.
Preferably the microfistula tube is made of absorbable material.
Any suitable biocompatible material may be used, provided it permits the adherence of a basement membrane to the inner surface of the microfistula tube, and permits host endothelial or epithelial cells to grow in and coat the inner surface, while permitting minimal tissue reaction. Thus, the microfistula tube may be placed into a body, but will be incorporated into surrounding tissue or absorbed by the body over time. The biological cellsxe2x80x94whose type will depend on the location where the microfistula tube is implantedxe2x80x94will provide a biological lining of the drainage pathway (i.e. microfistula) formed within the body by the microfistula tube, and inhibit the wound healing processes that would tend to occlude the drainage pathway. These cells will also reduce rejection effects. The biological cells, which will eventually form a permanent or long-lived endothelial, epithelial or similar lining of the drainage pathway formed by the microfistula tube minimize the tendency for fibroblast proliferation and the occlusion of the pathway. Consequently a microfistula tube size smaller than has been feasible with prior art devices or techniques may be employed, thereby reducing the risk of overdraining the aqueous fluid.
Preferably the biological cells are endothelial or trabecular meshwork cells.
Preferably the microfistula tube is made of gelatin or collagen.
By using a substance such as gelatin or collagen the mechanical and absorption properties of the tube may readily be manipulated, and the microfistula tube given the required rigidity and absorption properties.
Preferably the microfistula tube is sufficiently rigid to allow ready insertion into a living body.
Preferably the microfistula tube is a tube with a circular cross-section.
Preferably the outer surface of the microfistula tube tapers towards its forward end to facilitate its insertion into body tissues. Thus, the microfistula tube may be narrower at the forward end so that it can more easily be pushed into the relevant tissues of the body.
Preferably the duct is provided with one or more generally rearwardly projecting barbs or a generally rearwardly projecting skirt. Preferably the one or more barbs or said skirt is near the forward end of said microfistula tube. Thus, once the microfistula tube is in place it will not easily be able to move back along the path of insertion and hence be dislodged.
Preferably the rearward end of said microfistula tube has thicker walls to provide improved area and strength to allow the microfistula tube to be pushed into place by pressing against the rear end of the microfistula tube.
Preferably the rearward end of the microfistula tube has an increased outer perimeter size to prevent the microfistula tube from advancing beyond the point of implantation.
Thus, the rear end of the microfistula tube has an increased perimeter or, when the microfistula is tubular, an increased outer diameter, both to provide a broader base against which pressure may be applied to insert the microfistula tube into body tissues, and also to prevent the microfistula tube from advancing further than the point of implantation.
Preferably the microfistula tube is adapted to form a passage from the anterior chamber to Schlemm""s canal, and has an interior diameter of between 100 and 200 xcexcm, and a length of between 1 and 3 mm.
More preferably the microfistula tube has an interior diameter of approximately 150 xcexcm and a length of approximately 2 mm.
Alternatively the microfistula tube is adapted to form a passage from the anterior chamber to the anterior subconjunctival space and has an interior diameter of between 100 and 400 xcexcm and a length of between 2 and 6 mm.
Preferably the microfistula tube has an interior diameter of between 250 and 350 xcexcm.
More preferably the microfistula tube has an interior diameter of approximately 300 xcexcm and a length of approximately 3 mm.
Alternatively the microfistula tube is adapted to form a passage from the anterior chamber to the episcleral vein, with an inner diameter of between 100 and 300 xcexcm and a length of between 7 and 14 mm.
Preferably the microfistula tube has an inner diameter of approximately 150 xcexcm and a length of approximately 10 mm.
In one embodiment the microfistula tube is adapted to form a passage from the vitreal cavity to the subarachnoid space of the optic nerve, and has an inner diameter of between 100 and 300 xcexcm and a length of between 3 and 12 mm.
Preferably the microfistula tube has an inner diameter of approximately 150 xcexcm and a length of approximately 6 mm.
Thus, the microfistula tube may be used in optical applications to shunt aqueous fluid from the anterior chamber into Schlemm""s canal, the subconjunctival space, or the episcleral vein, or from the vitreal cavity to the subarachnoid space of the optic nerve.
According to second broad aspect of the present invention there is provided a microfistula tube implantation system including:
a microfistula tube as described above; and
a surgical instrument including an outer tube for penetrating body tissue,
an inner tube, and
an innermost rod,
wherein said outer tube, said inner tube and said innermost rod are coaxial, said outer tube is adapted to receive said microfistula tube, whereby the inner tube may be used to push the microfistula tube into position and the innermost rod provides mechanical support during implantation of the microfistula tube.
Thus, the outer tube can be used to penetrate body tissues (for example a cornea), and the inner tube can then be used to push the microfistula tube forward and out of the forward end of the outer tube. The innermost rod may be moved with the inner tube until the microfistula tube is in its final position, and then the innermost rod may be withdrawn, followed by the inner tube. The outer tube may then be withdrawn from the body.
Preferably said microfistula tube is adapted to receive said innermost rod.
Preferably the outer tube is a hypodermic-type tube.
Preferably the inner tube is blunt-ended.
Preferably the outer tube is of stainless steel.
Preferably the inner tube is of stainless steel.
Preferably the innermost rod is of tungsten.
Preferably the surgical instrument is adapted to be attached to an ultramicrosurgical system.
Preferably the surgical instrument is adapted to be manipulated by electric motors.
Thus, the surgical instrument is adapted to deliver the microfistula tube to the required location. For greatest precision, the surgical instrument is used with a microsurgical system powered by electric motors and the operational procedures are performed under an operation microscope and gonioscopic observation.
According to third broad aspect of the present invention there is provided a microfistula tube implantation system including:
a microfistula tube as described above; and
a surgical instrument including an outer tube for cutting and penetrating body tissue, and
an inner rod,
wherein said outer tube and said inner rod are coaxial, said outer tube is adapted to receive said microfistula tube and said inner rod, and said outer tube has a sharp forward end for cutting body tissue, whereby the outer tube may be used to create a passage to an implantation site for said microfistula tube, said inner rod may be used to position a microfistula tube at said site, and said inner rod and outer tube may be withdrawn from said site leaving said microfistula tube in position at said site.
Preferably the outer tube is a hypodermic-type tube.
Preferably the outer tube is of stainless steel.
Preferably the inner rod is of stainless steel.
Preferably the surgical instrument is adapted to be attached to an ultramicrosurgical system.
Preferably the surgical instrument is adapted to be manipulated by electric motors.
According to fourth broad aspect of the present invention there is provided a method for the implantation of a microfistula tube including:
introducing into the vicinity of a desired implantation location an implantation system as described above with said microfistula tube mounted on the innermost rod,
pushing the microfistula tube out of the outer tube and into a desired location by means of the inner tube, the rod moving in unison with the inner tube and the microfistula tube,
withdrawing the surgical instrument from the body.
Preferably the rod is withdrawn from the microfistula tube before the inner tube is withdrawn.
Preferably the rod and inner tube are withdrawn into the outer tube before the inner tube, outer tube and rod are withdrawn from the body.
Preferably the desired location is the anterior chamber.
According to fifth broad aspect of the present invention there is provided a method for the implantation of a microfistula tube including:
forming the passage with said outer tube of said implantation system as described above with said microfistula tube in said outer tube forward of said inner rod,
advancing said microfistula tube to said implantation site with said inner rod,
withdrawing said outer tube,
withdrawing said inner rod, and
withdrawing the surgical instrument.
Preferably the method includes withdrawing the outer tube partially, then withdrawing said inner rod partially, followed by withdrawing said inner rod and outer tube in unison.
Preferably the partial withdrawal of the outer tube continues until said forward of said outer tube is in the anterior chamber.
Preferably the method includes rotating said outer tube with a reciprocating motion while forming said passage to aid said cutting of said tissue.